Mold for producing a model of a tooth

ABSTRACT

The invention relates to a mold for producing the model of a tooth from a dental impression ( 28 ), comprising a peripheral wall ( 12 ), a model plate ( 38 ) which is tightly arranged on the top thereof and an impression spoon ( 14 ) bearing the dental impression ( 28 ). Said spoon is tightly inserted into the lower end of the peripheral wall ( 12 ). The hollow cavity ( 42 ) thus obtained is filled with molding material to give a highly precise tooth model requiring no further mechanical processing.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a mould for producing a tooth model from adental impression.

2. Background Art

Such moulds are known in the form of cup-shaped formed bodies.

To produce a tooth model from a dental impression, the dental impressionis filled with a plastic modelling material which hardens. Immediatelyafter filling the dental impression with the modelling material in rarecases, while the modelling material is still soft, a mostly rubber-likemould is applied to the peripheral wall of the dental impression inorder, by filling the mould up to a predetermined height, to obtain abase on the tooth model.

To produce artificial teeth, said base is trimmed parallel to theocclusal plane mechanically by grinding; the result is a so-calledtoothed rim made of modelling material.

Then a drill and a twist drill are used to drill blind holes in the baseof the toothed rim, in each case under the teeth to be restored,adjacent teeth or antagonists, and metal pins are introduced andpreferably glued into the blind holes.

After subsequent isolation of the base mostly using an alginate-basedisolating material, the toothed rim with the glued-in pins is basallyaligned and introduced into a mould, which is filled to a height ofaround two centimeters with preferably the same plastic modellingcompound, until the base of the toothed rim is just completely wetted bythe plastic modelling compound. Said compound after it has hardenedforms the base for the toothed rim; toothed rim and base together formthe finished tooth model.

After hardening and mechanical trimming of the base, the toothed rim issawn in each case at right angles to the tangent predefined by theindividual tooth groups right down to the base such that the model teethto be restored, neighbouring teeth, maxillomandibular segments or anyother model teeth or model tooth groups may be individually removed fromthe base and precisely repositioned by means of the pins.

Such a saw-cut model is a prerequisite for producing any type ofartificial tooth from dental impressions.

Another way of producing model bases is such that the parallel-trimmed,conventionally produced toothed rims are provided in a special drillingapparatus with the blind holes for the pins and at the same timemirror-image holes are drilled into a prefabricated base plate made ofplastic material for receiving the pins, which are to be glued into thetoothed rim, together with the toothed rim. Removal of the preparedteeth is effected by the conventional saw-cut technique. Although thisdispenses with the outlay for processing a second plastic modellingcompound for producing the base, expensive equipment is necessary.

A particular problem associated with producing tooth models, inparticular toothed rims, is the filling of the mostly hydrophobic dentalimpression with the hydrophilic modelling material, usually dentalplaster. The narrow indentations of the individually moulded teeth,undercuts occasioned by the tooth shape and fine delineation of thetextured surface of the teeth in most cases promote bubble formation inthe tooth model which often makes it necessary to produce a second toothmodel. Such a second tooth model however is mostly of an inferiorquality to the first tooth model because the removal of the latter fromthe dental impression simultaneously leads to the breaking-off of fineedges and surface structures as well as fine interdental lamellae orlamellae in the sulcus region.

In addition, defects attributable to the shaping by the dentist toobtain the dental impression are frequently only detectable on the toothmodel. Because of the elaborate process of producing the latter,however, defects are mostly not spotted until several days after takingthe impression from the patient. In many cases the patient has to bebrought back for a new impression to be taken, which entails a highoutlay and often leads to poorer impression results because a commonconsequence of the initial treatment is a tendency to bleed during thefollow-up treatment.

SUMMARY OF THE INVENTION

The object of the invention is to provide a mould for producing a toothmodel from a dental impression, which enables a simpler processingtechnique involving only a lower number of working steps and by means ofwhich the number of error sources is reduced and tooth models of greaterprecision are obtained.

In the mould according to the invention, the bottom wall of the mould isformed by the impression tray used to produce the dental impression,wherein the dental impression for producing the tooth model remains onthe impression tray.

The impression tray at least in portions of its outer surface has aprecisely predetermined geometry and may without reworking be connectedprecisely and tightly to the peripheral wall of the mould.

As will become even clearer from the detailed description below,production of a tooth model using the mould according to the inventionsaves time and costs. In particular, compared to conventional productionof the toothed rim, there is no need for mechanical trimming, drillingof the blind holes for the pins or manufacture of the base plateinvolving repeat processing of modelling material, nor is there any needfor expensive equipment for producing the toothed rim.

The use of the mould according to the invention is to a large extenterror-tolerant and may be extensively automated.

The invention also makes it possible for the tooth model to be produceddirectly at the dental surgery. All the dentist need do, afterproduction of the dental impression, is clamp the used impression traytogether with the impression itself into the peripheral wall andintroduce into the mould thus obtained an adequate amount of modellingmaterial over the dental impression. Only the tooth model thus obtainedis then passed on to the dental technician.

Producing the tooth model at the dental surgery also has the advantagethat minor defects of the dental impression are easier to spot on thetooth model and the dentist in said case may immediately take anotherimpression from the patient before the latter leaves the premises.

A mould is tightly closed on all sides.

The mould during filling may therefore be acted upon by a pressure belowor above atmospheric. The former has the advantage of keeping bubbleformation very low. In both cases, the modelling material flows welleven into small interstices.

It is moreover possible for a mould prior to introduction of themodelling material, to be thoroughly rinsed with a wetting agent oranother treatment medium so that the surface of the impression isoptimally prepared for subsequent contact with modelling material.

A mould also easily allows the production of a tooth model which, at itsbase side, is already flat without machining of the modelling material.

In said case, the development of the invention is advantageous in viewof a bubble-free quality of the—during casting—top end face of the toothmodel.

The development of the invention also serves to achieve bubble-free,complete filling of the mould with modelling material.

The effect achieved by the development of the invention is that thefeeding of modelling material is automatically terminated when the mouldis completely full of modelling material.

Sealing connections may be realized in a simple and reliable mannerbetween the peripheral wall and the impression tray and/or theperipheral wall and the model plate.

The development of the invention is advantageous in view of precise,reproducible positioning of a model plate on the peripheral wall.

The development of the invention allows the realization of a tooth modelwhich may then, by means of saw cuts effected transversally relative tothe mandibular arch, be made into a saw-cut model in which individualteeth or tooth groups are removable and precisely repositionable.

For said purpose positioning pins may be used, which are embedded in thetooth model and in each case have a positioning portion projecting abovethe tooth model.

The blind recesses in the model plate may also be made permeable to gasso that the modelling material may penetrate into the blind recesseswhen the modelling material is introduced under pressure aboveatmospheric. When it is introduced under pressure below atmospheric, airsituated in the blind recesses is extracted. The result is the formationon the tooth model of positioning pegs, which are complementary to theblind recesses.

The development of the invention allows reproducibly precise feeding ofthe modelling material to the mould cavity.

In said case, the development of the invention guarantees that no airbubbles are trapped between the modelling material and the dentalimpression.

The development of the invention makes it possible, while usingidentical basic components, to realize moulds of differing height,thereby also enabling tooth models of differing height to be produced inan identical manner.

The development of the invention in a simple manner allows a tightbracing of the peripheral wall with the model tray and optionally themodel plate, particularly also in cases where impression tray as well asoptionally model plate and peripheral wall have cooperating positivelocking means which ensure, on the one hand, exact alignment of theimpression tray in the peripheral wall and, on the other hand, efficientsealing of the mould cavity.

The development of the invention in said case guarantees that, despitethe slot provided in the peripheral wall, efficient sealing of the mouldcavity is achieved.

The developments of the invention allow external visual checking of thefilling of the mould cavity with modelling material, particularly giventhe use of dyed modelling materials.

The effect achieved by the development of the invention is that theouter surface or outer lateral surface of the tooth model has a shapewhich is suitable for exact positioning in an articulator or similarapparatus without the outer surface of the tooth model having to be cutfor said purpose. Thus, when using a mould according to the invention,there is no longer any troublesome generation of plaster dust or dustfrom other modelling materials in the dental laboratory.

Embodiments of the invention are described in detail below withreference to the accompanying drawings. Said drawings show:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: a plan view of a mould for producing tooth models together witha diagrammatically illustrated device for filling the mould withmodelling material, wherein part of a model plate forming the top of themould is broken away;

FIG. 2: a transverse section through the mould shown in FIG. 1 along thecranked cutting line II—II of FIG. 1;

FIG. 3: a plan view of the model-side boundary surface of the modelplate of FIGS. 1 and 2;

FIG. 4: a longitudinal section through the model plate along the cuttingline IV—IV of FIG. 3;

FIG. 5: a plan view of the model-side boundary surface of the modelplate with a sawn toothed rim of a mandibular arch carried by the modelplate;

FIG. 6: a plan view of the holder-side boundary surface of the modelplate shown in FIG. 5;

FIG. 7: a section similar to FIG. 2 through a modified mould used toproduce higher tooth models;

FIG. 8: a view similar to FIG. 3, which shows a modified model plate;

FIGS. 9 and 10: sections through further modified model plates, whichare similar to the section of FIG. 2; and

FIG. 11: a view similar to FIG. 1 but showing a modified device forfilling the mould with modelling material.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 and 2 show a mould for producing tooth models, which is denotedas a whole by 10. The mould 10 has a peripheral wall 12, the bottomportion of which is complementary to the outer surface of an impressiontray 14.

The illustrated impression tray 14 is a tray for producingsupramaxillary impressions and comprises a bottom wall 18, having amiddle wall portion 20 modelled on the soft palate, and a boundary wall22 extending in peripheral direction. Soldered onto the edge of the wallportion 20 and the top end of the boundary wall 22 are wire pieces 24and 26, which create undercuts, against which a dental impression 28made e.g. of silicone, alginate or the like is latched.

Provided in the bottom third of the boundary wall 22 is a longitudinallyextending groove 30, into which a longitudinally extending rib 32provided on the inner surface of the peripheral wall 12 positivelyengages.

A seal 34 is supported via the rib 32 by the peripheral wall 12 andcooperates with the outer surface of the peripheral wall 22. Both byvirtue of said seal and also by virtue of the keyed connection betweengroove 30 and rib 32 an efficient sealing and precise positioningbetween peripheral wall 12 and impression tray 14 are achieved.

As is clearly evident from FIG. 2, the contour of the inner surface ofthe peripheral wall 12 corresponds to the contour of the outer surfaceof the boundary wall 22, which likewise assists sealing and goodpositioning. The outer surface of the peripheral wall 12 moreover vergessmoothly into the outer surface of the impression tray 14.

The outer surface of the peripheral wall 12 extends with an obliquelyoutward slope so that the thickness of the peripheral wall 12 increasesin an upward direction.

A marginal recess 36 extending in longitudinal direction of theperipheral wall 12 is set back from the top end face of the peripheralwall 12. A bottom portion of a model plate 38 engages positively intothe marginal recess 36. Inserted into the bottom of the marginal recess36 is a seal 40, which cooperates with the edge of the, in FIG. 2,bottom boundary surface of the model plate 38.

The peripheral wall 12, the impression tray 14, the dental impression 28carried by the latter and the model plate 38 therefore together delimitan outwardly sealed mould cavity 42.

To enable fitting of the peripheral wall 12 on the impression tray 14,the, in FIG. 1, bottom wall portion of the peripheral wall 12 isprovided with a slot 44. The peripheral wall 12 is made of asubstantially rigid yet slightly elastically deformable plastic materialso that the peripheral wall 12 by virtue of the elastic expansionenabled by the slot 44 may be clipped onto or removed from theimpression tray 14.

The, in FIG. 1, bottom wall portion of the peripheral wall 12 has in thevicinity of the slot 44 two dovetail parts 46, 48, the dovetail faces 50of which widen in a downward direction. When a clamping part 52 providedwith complementary inner dovetail faces 54 is slipped onto the dovetailfaces 50, the peripheral wall 12 is drawn together at the slot 44 andhence applied tightly and sealingly against the outer surface of theimpression tray 14. At the same time, a seal 53 lying between thelateral faces of the slot 44 is placed under initial tension.

Two connection pieces 56, 58 are provided in the outer-lying regions ofthe bottom wall portion of the peripheral wall 12. of said connectionpieces the left is tightly connected to the outlet of a reservoir 60containing a liquid modelling material (e.g. plaster). A ventilationconnection of the reservoir 60 is connected by an adjustable throttle 62to the environment.

The connection piece 58 contains a stopper 64, which is permeable to gasbut acts as an obstruction to modelling material. The connection piece58 is connected by the stopper 64 to the suction opening of a suctionpump 66. The outlet of the latter is connected likewise to the ambientatmosphere.

As is clearly evident from FIGS. 1, 2 and 6, the boundary surface of themodel plate 38 remote from the mould cavity 42 carries radialpositioning ribs 68, which have a substantially triangular basic crosssection and slope down towards the middle of the model plate 38. Thepositioning ribs 68 cooperate with complementary positioning grooves ofa non-illustrated holding part, as is customary with divided magneticbase systems. The holding part in turn is clamped into the articulatoror a machining apparatus of the dental technician.

The outer-lying side of the model plate 38 moreover carries inside aflat indentation 70, which is open towards the edge, a disk-shapedfixing part 72, which has a shaft 73 made of magnetic or magnetizablematerial embedded in the model plate and cooperates with a counterpartfixing part, which is carried by the holding part and likewise made ofmagnetic or magnetizable material. In said manner the model plate 38 isreleasably fixed on the holding part.

The procedure for producing a tooth model using the mould describedabove is as follows:

The impression tray 14 carrying the dental impression 28 is latched intothe peripheral wall 12 and the model plate 38 is inserted into the topend of the peripheral wall 12. Then the clamping part 52 is slipped ontothe dovetail parts 46, 48 so that the above-mentioned parts are bracedwith one another.

The suction pump 66 is then set in operation and the mould cavity 42 isfilled with liquid modelling material at a rate predetermined by theadjustment of the throttle 62. Alternatively, the modelling material maybe fed in under pressure above atmospheric, as will be described ingreater detail further below with reference to FIG. 11.

Preferentially, the mould cavity 42 is first evacuated and then themodelling material is fed in under pressure above atmospheric. Acompressor 104 and a {fraction (2/2+L )}-way and a {fraction (3/2+L)}-way magnetic valve 106 and 108 respectively, which are operated by asuitable control unit 110, are used for said purpose. Pressureregulators 112 and 114 are used to preselect the pressure below andabove atmospheric in the mould cavity 42. Said variant is shown bydashes in FIG. 1.

The filling operation may be visually checked through the model plate 38and/or the peripheral wall 12. Additional shaking or vibrating of themould 10 may even out the filling operation and cause any air bubblestrapped under modelling material in the indentations of the dentalimpression 28 to rise. This is preferably effected by means of amechanical vibrator 74, which is mechanically coupled to the mould 10 inthe manner indicated by dashes in FIG. 1.

At the end of the filling operation the liquid modelling material thenreaches the stopper 64. As the modelling material is unable to penetratethe stopper, the suction pump 66 then operates against a closed volume,which is acoustically easily perceptible. Where desired, it is alsopossible to connect to the line extending between the stopper 64 and thesuction pump 66 a pressure monitor 76, the output signal of which may beused to sound an alarm.

Once the modelling material has hardened, the clamping part 52 isslipped down off the dovetail parts 46, 48. The model plate 38 may thenbe lifted in an upward direction from the impression tray 14 and thedental impression 28 carried by the latter.

When, prior to filling the mould cavity 42, positioning pins 78 havebeen inserted in the model plate 38 at points where the finished toothmodel 80 is later to have removable segments or positioning pins, it ispossible in the manner shown in FIG. 5 then to produce said segments bymeans of saw cuts 82 so that the corresponding maxillomandibularsegments are individually removable from the model plate 38 andsubsequently also precisely repositionable there.

The positioning pins 78 each have an anchoring portion 84, which isintegrally cast in the modelling material and for the purpose ofimproving the frictional engagement is provided with a knurl comprisinggrooves or the like. The positioning pins 78 moreover have truncatedcone-shaped positioning portions 86, which are complementary to blindrecesses 88 provided in a grid arrangement on the boundary surface ofthe model plate 38 directed towards the mould cavity. FIG. 5 shows fourdifferent removable segments 90 a, 90 b, 90 c and 90 d of the toothmodel 80, which correspond to two cavities set back from the occlusalsurface, one truncated cone-like crown preparation and one lateralcavity of a tooth.

In the embodiments described below, mould parts which have already beendescribed above with reference to FIGS. 1 to 6 are once more providedwith the same reference characters. Said mould parts are also notdescribed in detail again below.

In the modified mould 10 shown in FIG. 7, a higher mould cavity 42 isachieved by inserting between the top end of the peripheral wall 12 andthe model plate 38 a distance element 92, the inside and outside edgecontour of which corresponds to the inside and outside edge contour ofthe top end of the peripheral wall 12. The bottom end face of thedistance element 92 is complementary to the top end face of theperipheral wall 12, and the top end face of the distance element 92 hasthe same geometry as the top end face of the peripheral wall 12.

A further seal 94 ensures sealing between the distance element 92 andthe model plate 38. It goes without saying that the dentist or dentaltechnician will stock a plurality of distance elements 92 so that theheight of the mould cavity 42 may be selected as close as possible torequired height of the tooth model. To adjust even larger mould cavities42, a plurality of such distance elements may also be stacked one on topof the other.

FIG. 8 shows a modified model plate 38, which is provided with a channel96. Said channel is connected by a stopper 98, which has the sameproperties as the stopper 64, to the suction side of the suction pump66.

In a further modification, the model plate 38 may also be provided witha plurality of such channels 96, which are provided [sic] in each caseby an associated stopper 98 to the suction pump 66.

When a model plate 38 has such channels 96, it is also possible todispense with the connection piece 58.

In the further modified model plate according to FIG. 9, the bases ofthe blind recesses 88 are formed by a material layer 100, which ispermeable to gas but impermeable to modelling material.

When a material layer 100 which is permeable to gas in one directiononly but blocks in the other direction (e.g. a semi-permeable membrane)is used, it is then also possible to evacuate the mould cavity of such amodified mould.

Instead of this, according to claim 10 very thin ventilation bores 102extending from the bases of the blind recesses 88 to the outer-lyingside of the model plate 38 may be provided.

When, instead of such a model plate-gripping mould 10 being operatedwith pressure below atmospheric, the modelling material is fed to themould under pressure above atmospheric, air may escape from the blindrecesses 88 and modelling material may penetrate into the blind recesses88. The result in said case is a plurality of positioning pegs formed onthe tooth model 80. Thus, no positioning pins are required.

When the mould 10 is acted upon by pressure above atmospheric, removabletooth model segments may also be subsequently defined simply by sawingthrough the tooth model at the required points. In an embodimentaccording to FIGS. 1 to 6, however, before introducing the modellingmaterial the points at which removable model segments are to be situatedhave to be fixed by suitably equipping the model plate 38 withpositioning pins 78.

The acting upon the mould cavity 42 with pressure above atmosphericduring introduction of the modelling material is achieved according toFIG. 11 by connecting the inlet of the throttle 62 to the outlet of acompressor 104. The stopper 64 is then flow-connected directly to theambient atmosphere.

Alternatively, a syringe or a mechanical feed pump may be used forfeeding in the modelling material under a pressure above atmospheric.

To prevent the model plate 38 from lifting off the peripheral wall 12when a pressure above atmospheric is admitted into the mould cavity 42,a keyed connection between model plate 38 and peripheral wall 12 may beprovided, e.g. a groove, which corresponds to the groove 30, in theouter surface of the assembly plate 38 and a rib, which corresponds tothe rib 32, carried by the side wall of the marginal recess 36.

In practice, work is carried out with a small number of differentlydimensioned impression trays 14 in order to cover differently sized jawsof patients. It goes without saying that the dentist or dentaltechnician will stock a corresponding number of differently sizedperipheral walls 12 and model plates 38 so that with the variousimpression tray sizes tooth models may be produced in the mannerdescribed above.

It goes without saying that prior to the feeding of the modellingmaterial the surfaces delimiting the mould cavity 42 are coated with asuitable release agent (e.g. release agent spray) so that the toothmodel after hardening easily detaches from said surfaces.

What is claimed is:
 1. Mould for producing a tooth model from a dentalimpression, having a bottom mould, which receives the dental impression(28) and comprises a peripheral wall (12) and a bottom wall, wherein theperipheral wall (12) is sealingly connected to an impression tray (14),which forms the bottom wall and carries the dental impression (28), anda model plate (38) is mountable sealingly onto the top end of theperipheral wall (12), characterized in that the peripheral wall (12) andthe model plate (38) together have at least two liquid openings (56, 58,96), which communicate with the mould cavity (42) delimited by theperipheral wall (12), the impression tray (14) and the model plate (38).2. Mould according to claim 1, characterized in that the liquid openings(56, 58, 96) of the mould-side boundary surface of the model plate (38)are adjacent.
 3. Mould according to claim 1, characterized in that theliquid openings (56, 58, 96) are connected to portions of the mouldcavity (42) which, in terms of flow, lie opposite one another.
 4. Mouldaccording to claim 1, characterized in that at least one of the liquidopenings (56, 58, 96) has a stopper (64, 98), which is permeable to gasbut not to modelling material.
 5. Mould according to claim 1,characterized in that the sealing connection between the peripheral wall(12) and the impression tray (14) comprises cooperating positive lockingmeans (30, 32), which are provided at the inside of the peripheral wall(12) and the outside of the impression tray (14) respectively.
 6. Mouldaccording to claim 1, characterized in that the sealing connectionbetween the peripheral wall (12) and the impression tray (14) comprisesmutually complementary surface portions of the inner surface of theperipheral wall (12) and of the outer surface of the impression tray(14).
 7. Mould according to claim 1, characterized in that the sealingconnection between the peripheral wall (12) and the impression tray (14)comprises at least one sealing element (34).
 8. Mould according to claim1, characterized in that the model plate (38) engages positively into arecess (36), which is provided in the top end face of the peripheralwall (12).
 9. Mould according to claim 1, characterized in that themodel plate (38) is provided with a plurality of undercut-free blindrecesses (88) arranged in a grid, wherein the latter preferably tapertowards the blind recess base.
 10. Mould according to claim 9,characterized by positioning pins (78), which comprise a positioningportion (86) complementary to the blind recesses (88) and an anchoringportion (84) firmly embeddable in the modelling material.
 11. Mouldaccording to claim 9, characterized in that a top portion of the blindrecesses, preferably the base of the blind recesses, is permeable togases but not to modelling material.
 12. Mould according to one of claim1, characterized in that at least one of the liquid openings (56, 58,96) is connected to a source (60) of modelling material.
 13. Mouldaccording to claim 1, characterized by a device (66; 104) for generatinga pressure difference between at least two of the liquid openings (56,58, 96).
 14. Mould according to claim 1, characterized by a lengtheningpart (92) for the peripheral wall (12) having a bottom end facecomplementary to the top end face of the peripheral wall and a top endface corresponding to the peripheral wall (12).
 15. Mould according toclaim 1, characterized in that the peripheral wall (12) has a slot (44)interrupting it in peripheral direction, and that a clamping device (46to 50) is associated with the slot (44).
 16. Mould according to claim15, characterized in that a sealing device (53) is associated with theslot (44).
 17. Mould according to claim 1, characterized in that theperipheral wall (12) is made of transparent or translucent material. 18.Mould according to claim 1, characterized in that the model plate (38)is made of transparent or translucent material.
 19. Mould according toclaim 1, characterized in that the inner surface of the top portion ofthe peripheral wall (12) has the shape of a polygon.